The BGS Lexicon of Named Rock Units — Result Details

Coleford Member

Computer Code: COFD Preferred Map Code: notEntered
Status Code: Full
Age range: Asturian Substage (CAS) — Asturian Substage (CAS)
Lithological Description: Predominantly a thick-bedded, coarse-grained sandstone of "Pennant"-type (lithic arenite), with subordinate interbeds of grey and green mudstone with ironstone concretions and coal. The sandstone is trough cross-bedded to planar bedded and beds commonly show erosive scours. Sandstone beds from beneath the Coleford High Delf seam are typically fine- to medium-grained. Coal seams up to 1.5 m thick are present within the succession.
Definition of Lower Boundary: Taken at the base of the lowermost sandstone of 'Pennant'-type (lithic arenite) of the Coleford Member. Occurs conformably above coarse-grained sandstone of the Trenchard Formation in the north of the Forest of Dean Coalfield and unconformably upon limestone and sandstone of the Pembroke Limestone Group in the south.
Definition of Upper Boundary: Taken at the base of the Brazilly Coal, present at the base of a grey mudstone- dominated succession of the Cinderford Member of the Grovesend Formation. The coal rests conformably upon thick-bedded, coarse-grained sandstone of the Coleford Member.
Thickness: 180m in the north to 300m in the south of the Forest of Dean Coalfield.
Geographical Limits: Restricted to the Forest of Dean Coalfield (SO 60).
Parent Unit: Pennant Sandstone Formation (PES)
Previous Name(s): Coleford Formation (-2106)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  Disused quarries and abandoned railway line at Meezy Hurst, proves a 300 m thick succession from the southern part of the coalfield, including the basal unconformity. Cleal & Thomas, 1996. 
Reference(s):
Cleal, C and Thomas, B A. 1996. British Upper Carboniferous stratigraphy. Geological conservation review series No. 11. [London: Chapman and Hall]. 
Waters, C N, Waters, R A, Barclay, W J, and Davies, J R. 2009. Lithostratigraphical framework for Carboniferous successions of Southern Great Britain (Onshore). British Geological Survey Research Report, RR/09/01. 184pp. 
Trotter, F M, 1942. Geology of the Forest of Dean and Iron-ore Field. Memoir of the Geological Survey of Great Britain. 
Waters, C N, Barclay, W J, Davies, J R and Waters, R A. In press. Stratigraphical framework for Carboniferous successions of Southern Great Britain (Onshore). British Geological Survey Research Report, RR/05/06. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E233